cylinder pressure

[grumpyvette]

the red line is normal, N/A engine pressure(no combustion)

the blue is useing NITROUS

thats where you get the extra torque from, the nitrous increased cylinder pressure!

notice thats also why the exhaust timing durration on a nitrous cam must be longer in durration to allow the extra exhaust volume to bleed off or youll have serious pumping losses while the engine fights the extra cylinder pressure that tends to restrict flow into the cylinder if you exhaust does not scavage correctly to allow the fast moving flow out of the cylinder to help drag the incoming charge into the cylinders

 

http://hcs.harvard.edu/~jus/0303/kuo.pdf

 

 

 

http://www.gmrc.org/gmrc/pdf/Beshouri5-AETCO.pdf

 

 

heres a crank angle chart for a 350 chevy

 

http://www.iskycams.com/ART/techinfo/ncrank1.pdf

 

heres a typical cam card

 

http://www.cranecams.com/?show=browseParts&action=partSpec&partNumber=119661&lvl=2&prt=5

 

 

 

notice that the cam exhaust opened on this cam at 83 degrees before bottom dead center, and by bottom dead center the cylinder has lost about 80%-90% of its peak pressure and if the exhaust is correctly designed it could even be negative pressure while exhaust scavaging takes place (look at the crank angle and the same degrees on the pressure curve, but keep in mind its a 720 degree cycle and some of those charts only show 360 of those 720 degrees) but if your running a stock restrictive exhaust , a mild cam and low compression like most stock engines and your spinning the engine at high rpms there still could be that 10%-20% pressure in the cylinder at bdc.

look also at the remaining cylinder pressure at each point in the graph, , its faily obvious that the exhaust must be long in durration and that the intake might need to open slightly later in the cycle to allow extra time for the exhaust to bleed off, and open the exhaust earlier in the cycle, thats why nitrous cams tend to have a wider LSA and longer exhaust durration compared to intake durration

 

if YOU look at the cylinder pressure curves youll see that the cylinder bleeds down quite rapidly as the piston moves away from tdc on the power stroke and falls even faster once the exhaust valve opens, if there is significant pressure left at bdc the engine won,t run very well at higher rpms, thats one of the reasons header scavaging and cam overlap and matching the exhaust timing and duration are so important to engine design

[dmyntti]

The red line appears to be straight compression line without any combustion. Notice that the peak it at 0 degrees crank angle. The blue line does appears to look like you would expect with compression. I have worked with an old superflow engine analyzer developing components for compressors. It is amazing how much difference port/valve flow has on the traces. I can't speak of cam timing because the compressors I worked with had a check valve style valve and you could not adjust valve timing.

[grumpyvette]

dmyntti

thanks for catching that, (I left out the NO COMBUSTION)